You can either:
a) Extract a new copy from the Win Me cab set (see later), or,
b) Download and install the MovieMaker update for Win Me using the
following link.
http://download.windowsupdate.com/msdownload/update/v3-19990518/cabpool/287564_C
357B6006425BFFD54868CA64F1A975D567C1451.EXE

b) having been my suggestion to you when you last posted this query.  Did
you read that reply and try it?  If yes, with what result?  If not, why
not?

wmmutil.dll is contained in WIN_16.CAB of the Win Me cab set and can be
replaced by booting to Safe Mode and using MSConfig | General | Extract
File and following the prompts.  The "cab" files are in the Win9x folder
on the Win Me CD and normally also in either Windows\Options\Cabs or
Windows\Options\Install.  See MS  KB 265371 - "How to Extract and Replace
a Protected File in Windows Me" (http://support.microsoft.com?kbid=265371)
for details of how to extract files from the cab set.

wmmutil.dll belongs in the Program Files\Movie Maker folder.